Segregation of chromium in CoOCr2O3 solid solutions and CoCr2O4 spinel phases studied by SIMS and ESCA

Sikora, I.; Stolze, F.; Hirschwald, W.

doi:10.1002/sia.740100808

Cited by 20 publications

(13 citation statements)

References 18 publications

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“…It has been shown that even trace-level silicon in ppm amounts leads to segregation-induced enrichment of YSZ surface layers. 17 A similar effect was observed for Ca.…”

Section: Intrinsic Chemical Effectssupporting

confidence: 80%

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Segregation in zirconia: equilibrium versus non‐equilibrium segregation

Nowotny

Sorrell

Бак

2005

Surface & Interface Analysis

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The present work considers the differences between the following two phenomena: equilibrium segregation, which is a thermodynamic phenomenon where the driving force is excess interfacial energy; and non-equilibrium segregation, which can be produced by phenomenological shocks applied to the solid surface. Fully stabilized cubic yttria-stabilized zirconia (YSZ) is used as the exemplar for these considerations. Equilibrium segregation in YSZ results in enrichment of the surface and near-surface layers in constituent elements, typically yttria and impurities. This segregation is an intrinsic material property and has an impact on the performance of zirconia at elevated temperatures. On the other hand, non-equilibrium segregation leads to a complex distribution of properties (structure and concentration gradients) that are determined by the experimental procedures used rather than being a material property. However, such non-equilibrium segregation can result in localized structural changes. The present paper also considers the effect of the gas phase on surface properties of metal oxides, including YSZ, and the surface dynamics of YSZ at temperatures below that required to reach equilibrium.

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“…It has been shown that even trace-level silicon in ppm amounts leads to segregation-induced enrichment of YSZ surface layers. 17 A similar effect was observed for Ca.…”

Section: Intrinsic Chemical Effectssupporting

confidence: 80%

“…14,15 The concentration gradient across the boundary layer typically may range across a few nanometres to several hundred. 17,18 It is widely appreciated that such impurity segregation in zirconia has a significant impact on its functionality.…”

Section: Impuritiesmentioning

confidence: 99%

Segregation in zirconia: equilibrium versus non‐equilibrium segregation

Nowotny

Sorrell

Бак

2005

Surface & Interface Analysis

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“…37,38 The effect of oxygen activity on the segregation-induced enrichment in oxides was reported by Black 39 Application of XPS and SIMS in surface analysis of Nbdoped TiO 2 annealed in controlled oxygen activity has shown that annealing in oxidizing and reducing conditions results in a strong enrichment and depletion of the surface in niobium, respectively. 40 Recently Sheppard et al 41,42 reported the effect of oxygen activity on niobium segregation in Nb-doped TiO 2 .…”

Section: Brief Literature Overviewmentioning

confidence: 97%

Niobium Segregation in Niobium-Doped Titanium Dioxide (Rutile)

2014

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This work determined the effect of niobium segregation on the surface and near-surface composition of Nb-doped TiO 2 , containing 0.18 atom % Nb and 0.018 atom % Nb, after annealing in the gas phase of controlled oxygen activity. The segregation-induced concentration profiles were determined using a range of analytical techniques of different depth resolution, including secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), Rutherford backscattering (RBS), and proton-induced x-ray emission (PIXE). The XPS analysis of the 0.18 atom % Nb specimen annealed at 1273 K in oxidizing conditions and showed segregation-induced niobium surface enrichment of 2.83 atom % and 2.35 atom % in p(O 2 ) = 75 kPa and p(O 2 ) = 10 Pa, respectively. However, annealing at 1273 K in strong reducing conditions, p(O 2 ) = 10 −10 Pa, leads to depletion of the surface layer in niobium to the level of 0.05 atom % (desegregation). The results of SIMS, RBS, and XPS are consistent. The derived theoretical model, explaining the effect of oxygen activity on niobium segregation, considers contribution from three driving forces of segregation, including (i) strain relaxation, (ii) the formation of a lowdimensional surface structure, and the (iii) electric field associated with the surface charge. The established effect of oxygen activity on niobium segregation/desegregation may be used as a technology for imposition of (i) controlled surface composition that is required to achieve enhanced performance of TiO 2 in solar-to-chemical energy conversion and (ii) chemically induced electric field required for charge separation.

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“…[8][9][10][11] Consequently, oxygen activity is one of the key properties that have a critical impact on oxygen non-stoichiometry and related concentration of defects. Therefore, modification of the nonstoichiometry (both in the bulk and at the surface) may be achieved through variation of the oxygen activity in equilibrium.…”

Section: Effect Of Oxygen Partial Pressurementioning

confidence: 99%

Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 3: Segregation induced interface properties

Nowotny¹,

Бак²,

Nowotny³

et al. 2005

Advances in Applied Ceramics

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The present paper considers segregation of lattice elements, including dopants and impurities, in oxide materials and its effect on the formation of concentration gradients within the interface layer. Segregation is discussed in terms of the effect of temperature and oxygen partial pressure on segregation induced enrichment of interfaces in oxide materials and related local properties. The phenomenon of segregation and its impact on surface composition is outlined for yttria-stabilised zirconia (YSZ), where it impacts upon the performance of zirconia at elevated temperatures. The difference between equilibrium segregation and non-equilibrium segregation is discussed. In the former case, the segregation induced data represent specific materials properties. In the latter case, non-equilibrium segregation leads to a complex distribution of concentration gradients and structures, which are a reflection of the applied experimental procedures rather than of material properties.

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Segregation of chromium in CoOCr₂O₃ solid solutions and CoCr₂O₄ spinel phases studied by SIMS and ESCA

Cited by 20 publications

References 18 publications

Segregation in zirconia: equilibrium versus non‐equilibrium segregation

Segregation in zirconia: equilibrium versus non‐equilibrium segregation

Niobium Segregation in Niobium-Doped Titanium Dioxide (Rutile)

Charge transfer at oxygen/zirconia interface at elevated temperatures: Part 3: Segregation induced interface properties

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